System, apparatus and method for acquisition of signals in wireless systems with adverse oscillator variations

ABSTRACT

In one aspect, a radio device comprises: an analog front end (AFE) circuit to receive and process an incoming radio frequency (RF) signal comprising a packet; an analog-to-digital converter (ADC) coupled to the AFE circuit to receive and digitize the processed incoming RF signal into a digital signal; a detector coupled to the ADC to detect a carrier frequency offset (CFO) in the digital signal based at least in part on a preamble of the packet; and a controller coupled to the detector. The controller may generate a compensation value for the CFO based on the detected CFO and cause one or more components of the radio device to compensate for the CFO using the compensation value.

BACKGROUND

In wireless systems, incoming radio frequency (RF) signals are receivedand processed to recover message information such as data, audio, videoor so forth. Many different operations are performed at RF frequenciesand lower frequencies, including at baseband.

Careful adherence to accurate frequency of operation is needed toproperly acquire and process incoming RF signals. There can be a varietyof factors, including environmental conditions such as operating at hightemperatures, that may lead to problems related to acquisition of RFsignals in wireless systems. As an example, high temperatures can causea variance in a local oscillator of a wireless device that may affectacquisition of signals/packets.

SUMMARY OF THE INVENTION

In one aspect, a radio device comprises: an analog front end (AFE)circuit to receive and process an incoming radio frequency (RF) signalcomprising a packet; an analog-to-digital converter (ADC) coupled to theAFE circuit to receive and digitize the processed incoming RF signalinto a digital signal; a detector coupled to the ADC to detect a carrierfrequency offset (CFO) in the digital signal based at least in part on apreamble of the packet; and a controller coupled to the detector,wherein the controller is to generate a compensation value for the CFObased on the detected CFO and cause one or more components of the radiodevice to compensate for the CFO using the compensation value.

In an example, the radio device further comprises an external crystaloscillator to provide an oscillation signal to a frequency generator.The frequency generator may be coupled to the external crystaloscillator to receive the oscillation signal and generate one or mixingsignals therefrom. The controller may send the compensation value to oneor more of the external crystal oscillator and the frequency generatorto cause the CFO compensation to occur. The controller may send thecompensation value to the external crystal oscillator when the detectedCFO exceeds a threshold value, and not send the compensation value tothe external crystal oscillator when the detected CFO is less than thethreshold value.

In an example, the controller is to generate a second compensation valuewhen a first packet is not acquired, the second compensation value tocompensate for a hypothetical CFO in the second packet. The controllermay generate a plurality of test compensation values, each of theplurality of test compensation values for a hypothetical CFO. The radiodevice may further include a plurality of correlators each to perform acorrelation on the second packet using one of the plurality of testcompensation values, and the controller may select one of the pluralityof test compensation values for use as the compensation value for athird packet. The radio device may further comprise one or more filters,where the one or more filters are to operate at a wider bandwidth whenthe plurality of correlators are used.

In another aspect, a method comprises: receiving, in a receiver, a RFsignal of a first packet; processing, in the receiver, the RF signalinto a baseband signal; obtaining a preamble of the first packet fromthe baseband signal; determining a CFO based at least in part on thefirst packet; and controlling one or more devices to compensate for theCFO to receive a second packet.

In an example, controlling the one or more devices comprises sending acompensation signal to an oscillator to cause the oscillator to adjust afrequency of operation. Controlling the one or more devices may furthercomprise sending a second compensation signal to a frequency generatorof the receiver to cause the frequency generator to adjust a frequencyof a mixing signal provided to a transmitter, the transmitter includedin a transceiver with the receiver.

In an example, determining the CFO comprises: extracting a first portionof the preamble; measuring the CFO based on the first portion; andgenerating a compensation value based on the CFO. Controlling the one ormore devices may include sending the compensation value to at least oneof a frequency generator of the receiver and an oscillator.

In an example, the method further comprises: in response to determiningthat the first packet is not acquired, generating at least one testcompensation value to compensate for a hypothetical CFO in the secondpacket; controlling the one or more devices using the at least one testcompensation value to compensate for the hypothetical CFO; andthereafter in response to acquiring the second packet using the at leastone test compensation value, further using the at least one testcompensation value to control the one or more devices to compensate forthe CFO.

In an example, the method further comprises: generating a plurality ofcorrelation values, each of the plurality of correlation valuesgenerated using one of a plurality of message contents obtained usingone of a plurality of test compensation values; selecting one of theplurality of test compensation values based at least in part on theplurality of correlation values; and using the selected testcompensation value to control the one or more devices to compensate forthe CFO.

In yet another aspect, a system comprises: a crystal oscillator togenerate a clock signal at an oscillation frequency; and a receivercoupled to the crystal oscillator. The receiver comprises: an AFEcircuit to receive and process an incoming RF signal comprising apacket; a digitizer coupled to the AFE circuit to convert the processedincoming RF signal into a digital signal; a detector coupled to thedigitizer to detect a CFO in the digital signal due to variation in theoscillation frequency, where the detector is to detect the CFO based atleast in part on one or more fields in a preamble of the packet; and acompensation circuit coupled to the detector to compensate for the CFOin the digital signal.

In an example, the compensation circuit comprises one or more of: anumerically controlled oscillator (NCO) to provide a frequency offsetthat is opposite to the CFO; and a sample control circuit to compensatea timing offset based at least in part on the CFO. The system mayfurther include a transmitter, where the controller is to control thetransmitter to compensate for the CFO during a communication with anaccess point, where the access point comprises a second transmitter totransmit the incoming RF signal comprising the packet. The controllermay determine a compensation value for the CFO based on the detected CFOand send the compensation value to the crystal oscillator to cause thecrystal oscillator to adjust the oscillation frequency of the clocksignal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a receiver in accordance with anembodiment.

FIG. 2 is a flow diagram of a method in accordance with an embodiment.

FIG. 3 is a block diagram of a portion of a baseband processor inaccordance with an embodiment.

FIG. 4 is a block diagram of a representative integrated circuit thatincorporates and embodiment.

FIG. 5 is a high level diagram of a network in accordance with anembodiment.

DETAILED DESCRIPTION

In various embodiments, a control system may determine a carrierfrequency offset (CFO) for an incoming wireless communication usinginformation included in a packet of the communication. While embodimentsherein are directed to carrier frequency offset detection andcompensation relating to variations in oscillator signals (and resultingdevice-generated clock signals), understand that the techniques hereinare usable for a variety of different causes of carrier frequencyoffsets such as other factors which can affect PPM of the crystal.

Furthermore while embodiments herein are discussed in connection withpacket-based wireless communications, other embodiments may be used indifferent wireless schemes. And while particular embodiments may be usedin connection with wireless local area networks (WLANs) such as inaccordance with a given IEEE 802.11 standard, other embodiments may beused for wireless wide area networks or other wireless communicationprotocols.

In typical wireless communication systems, communication is in the formof bursts of packets where each such packet typically includes apreamble, a header, and a payload (amid potentially other information).The preamble of the packet is used by the receiver for the purposes ofpacket detection, measurement of carrier frequency offset, measurementof timing offset, and so forth. For example, in a WLAN—OrthogonalFrequency Division Multiplexing (WLAN-OFDM) system, the preamble portionof the packet includes a Legacy—Short Training Field (L-STF also calledShort Preamble) and a Legacy—Long Training Field (L-LTF also called LongPreamble). By using a L-STF, a coarse CFO estimate can be obtained andby using a L-LTF, a fine CFO estimate may be obtained. As such thispreamble information can be used for the purpose of the estimation ofcarrier frequency offset (also may also be used for other purposes likechannel estimation, etc.).

Referring now to FIG. 1 , shown is a block diagram of a receiver inaccordance with an embodiment. As shown in FIG. 1 , receiver 100 may beimplemented, in some cases, as a single semiconductor die receiver asincluded within an integrated circuit (IC). In such embodiments, allcircuitry shown in FIG. 1 with the exception of an external antenna 105and an external oscillator 180 (e.g., a crystal oscillator) may beimplemented on the single semiconductor die.

In the embodiment shown, incoming radio frequency (RF) signals arereceived via antenna 105 and provided to a signal processing pathincluding a low noise amplifier (LNA) 110. After appropriateamplification here, the incoming RF signals are provided to an analogfront end (AFE) circuit 120. In various implementations, AFE circuit 120may include various filtering, gain circuitry and so forth, including ananalog filter 122. As will be described herein, in certain instances thebandwidth of this filter may be dynamically controlled in the presenceof significant CFO. Further as shown, AFE circuit 120 includes a mixer125 configured to downconvert an RF signal to a lower frequency signal,e.g., an intermediate frequency (IF) signal such as a low-IF signal,zero IF signal, or other lower frequency signal.

To this end, mixer 125, which in some cases may be a complex mixer, isconfigured to downconvert the incoming RF signals using a mixing signalhaving a mixing frequency, shown as mixing signal (f_(LO)) received froma frequency generator 170. As one example, frequency generator 170 maybe a local oscillator (LO) that may be implemented as a phase lockedloop (PLL). In embodiments herein, frequency generator 170 may generatethe mixing signal using an incoming oscillator signal, f_(x0), receivedfrom external oscillator 180. As described herein, there may bepotentially significant temperature variation in oscillator 180, forwhich embodiments may be configured to compensate.

Still referring to the signal processing path of receiver 100, thedownconverted signals output from AFE circuit 120 are provided to adigitizer, shown in FIG. 1 as an analog-to-digital converter (ADC) 130,which digitizes the signals. In turn, these digitized signals, which maybe at baseband, are provided to a baseband processor 140. Although shownas a standalone baseband processor in the FIG. 1 embodiment, basebandprocessor 140 in some cases may be implemented within a digital signalprocessor (DSP).

After various baseband processing, including filtering, digital mixing,decimation and so forth, resulting baseband-processed signals may beprovided to a demodulator 150 that demodulates these signals. Indifferent implementations, one of a variety of demodulation schemes maybe used. For purposes of discussion herein, assume that demodulator 150is configured to perform orthogonal frequency division multiplexing(OFDM) demodulation. The resulting demodulated signals may be outputfrom demodulator 150 and provided to further downstream processingcircuitry, such as an audio processor (not shown for ease ofillustration in FIG. 1 ).

To compensate for variations in oscillator frequency, baseband processor140 may include a carrier frequency offset (CFO) detector 145. Althoughshown as being included within baseband processor 140, in otherimplementations CFO detector 145 may be a separate component. As will bedescribed further herein, CFO detector 145 may be configured to detect,at baseband, CFO in received signals. Based at least in part on thisdetected CFO, a compensation circuit 142, also shown as being includedin baseband processor 140, may compensate for the detected CFO in thecurrent packet being processed (and following packets).

CFO detector 145 also may communicate any detected CFO to a controller160. Although controller 160 is shown as a separate component in FIG. 1, it is possible in some implementations for this controller to beincluded within a baseband processor (or as part of a DSP in someimplementations). In any event, controller 160 may include eitherdedicated or programmable hardware circuitry configured to controlcompensation of CFO, among other functions. To this end, controller 160may include or be coupled to a non-volatile storage or othernon-transitory storage medium to store instructions and data usable forperforming CFO detection and compensation as described herein.

As further detailed in FIG. 1 , controller 160 includes a calibrationcircuit 165. In embodiments herein, calibration circuit 165 may beconfigured to calibrate for CFO. Thus in response to CFO informationreceived from CFO detector 145, calibration circuit 165 may determineone or more control values for use in controlling CFO. Calibrationcircuit 165 may communicate such CFO control information to one or moreof frequency generator 170 and/or oscillator 180. Based on thisinformation, dynamic real time CFO compensation may occur, e.g., due toCFO caused by temperature variation of oscillator 180.

Furthermore, understand while in the embodiment of FIG. 1 , only areceiver signal processing path is shown for ease of illustration, suchreceiver may be part of a wireless transceiver further includingtransmit capabilities. In such cases, carrier frequency offsetcompensation further may be performed for the transmit path, e.g., byway of appropriate control of a frequency generator (either frequencygenerator 170 or another such frequency generator) that provides amixing signal used for upconverting transmission signals to anappropriate RF frequency. Understand that while shown at this high levelin the embodiment of FIG. 1 , many variations and alternatives arepossible.

In embodiments, CFO/PPM variation introduced due to high temperature ata crystal (or other oscillator) can be measured using preambleinformation of a packet. The order of CFO that may be observed can beunderstood with the following examples. A parts per million (PPM)variation of ‘+50’ from a nominal level at the crystal causes frequencyoffsets of 120 kilohertz (kHz) and 250 kHz in systems operating atfrequencies of 2.4 gigahertz (GHz) and 5 GHz, respectively. Similarly, aPPM of ‘+200’ at the crystal causes frequency offsets of 480 kHz and 1megahertz (MHz) in systems operating at frequencies of 2.4 GHz and 5GHz, respectively.

In a WLAN system, a receiver of a station can make use of a preamble ofpackets received from an access point (AP) to measure the CFO/PPM of thestation. Note that a variety of different packets from the AP such asbeacons (which are transmitted periodically (based on a delivery trafficindication message (DTIM)), packets transmitted to it, and/or packetstransmitted to other stations, can be used to determine CFO. In aparticular embodiment, received packets may be OFDM or direct sequencespread spectrum (DSSS) modulated packets.

It may be assumed that the temperature at the AP is not changing andremains the same. This implies that no CFO is observed at the AP, or theCFO remains the same for packets originating from the AP. Note that theCFO measured at the station based on preamble information may accountfor any CFO at the AP, if present. The measured CFO is still valid forcompensation even if there is CFO at the AP, since this is the same APwith which the station communicates.

Different implementations may be used for various wireless systems thatuse protocols like WLAN-OFDM, WLAN-DSSS, and Bluetooth, as examples. InOFDM WLAN systems, the CFO that can be measured on L-STF information ofa prefix is in the range +/−625 kHz, and from L-LTF information of aprefix is in the range +/−156.25 kHz. So the acquisition range is +/−625kHz. In systems where integer frequency offset estimation/correction isused, the acquisition range may be higher. Since a baseband clock signalis derived from the LO, the CFO and timing offsets in OFDM systems arein locked mode.

In DSSS WLAN systems, the CFO can be measured on a SYNC field of apreamble. CFO and timing offsets are not in locked mode as in OFDMsystems and can be resolved using the corresponding sampling clock. Inan embodiment where the wireless communication system is Bluetooth LowEnergy, a master broadcasts packets when it is in advertising modebefore establishing a connection with the slave. In a Bluetooth system,the master device and slave device act as AP and station respectively,when compared to a WLAN system. In a Bluetooth system, namely aBluetooth Low Energy (BLE) system, a packet structure includes apreamble, access address and payload. In an embodiment, CFO and timingoffsets may be measured on the access address of the packet. Note thatfrequency tracking and time tracking algorithms may also be operative onthe entire portion of the packet, as a frequency offset measured at thestart of the packet is used for compensation on the remaining portion ofthe packet. Frequency tracking and timing tracking algorithms may beused in systems having varying frequency offset (during the portion ofthe packet). Note that in a WLAN-OFDM case, the training fields (L-STF,L-LTF) are provided with repetitive portions. The phase offset betweenthe repetitive portions in the presence of CFO is used tomeasure/estimate the CFO. In another example where the protocol ofcommunication is Bluetooth and GFSK modulation is used, the fixed phaseoffset observed in the angle domain (or phase domain) can be used tomeasure the CFO.

Referring now to FIG. 2 , shown is a flow diagram of a method inaccordance with an embodiment. As shown in FIG. 2 , method 200 is amethod for compensating for carrier frequency offset. As such, method200 may be performed by control circuitry, such as a CFO detector and aCFO calibration circuit as described above with regard to FIG. 1 . Assuch, method 200 may be performed by hardware circuitry, firmware,software, and/or combinations thereof.

As illustrated, method 200 begins by receiving and processing anincoming packet (block 210). Although embodiments are not limited inthis regard, assume that the incoming packet (or frame, more generally)is communicated within a given RF signal and received in a receiveraccording to an OFDM modulation scheme and includes a preamble, aheader, and a data payload. This packet processing may be performed in asignal processing path such as shown in FIG. 1 , to receive and processan incoming RF signal, downconvert the processed RF signal, digitize thedownconverted signal, and then provide the digitized signal to abaseband processor. In turn, the CFO detection and compensation may beperformed at least in part at baseband.

Continuing with method 200, next it may be determined whether the packetis able to be acquired (diamond 220). Such acquisition may be performedusing well-known techniques to acquire a signal using predeterminedinformation present in a preamble of the packet. Here, the acquisitionof the frame may be treated as successful, only if a cyclic redundancychecksum (CRC) check on decoded data results in a CRC pass. Theacquisition process may include various steps starting from receivingand processing the frame to checking the integrity of the decoded datausing the CRC check. If acquisition is successful, the control path isto block 230. At block 230 the packet preamble may be extracted. Then atblock 240 a carrier frequency offset may be determined based at least inpart on certain information present in the preamble. Such determinationof CFO may be performed in a CFO detector and may be based on comparisonof received preamble information to expected information, e.g., apredetermined prefix pattern included in a preamble of an OFDM packet.

As one example, CFO computation may be done as follows: in the case ofL-STF, 10 repetitions are present with total of 160 samples over aduration of 8 microseconds (usec) (with a sampling rate of 20 MHz). Eachrepetition has 16 samples, implying that {x(n), x(n−16)},{x(n−1),x(n−17)}, . . . {x(n−15),x(n−31)} samples are the same whenconsidering a set of 32 samples. At the receiver in the presence offrequency offset, if y(n) is received as x(n), then y(n−16) will bereceived as x(n)exp(j*2*pi*(fc/fs)*16). The phase shift computed betweensample y(n) and y(n−16) gives the CFO (fc is the only unknown term whichis CFO and fs is sampling rate which is 20 MHz).

Still with reference to FIG. 2 , the OFDM packet may be compensatedwithin the baseband circuit for the determined CFO at block 245. Next itmay be determined at diamond 250 whether a carrier frequency offset thusdetermined exceeds a threshold. As an example, a threshold may be set ata particular value of parts per million (PPM), e.g., betweenapproximately +100 PPM and −100 PPM. If it is determined that thiscarrier frequency offset does not exceed the threshold level, no furtheroperations occur with regard to carrier frequency offset compensationfor the current packet and control passes back to block 210 for a nextreceived packet. Thus, as shown in FIG. 2 , CFO estimation andcorrection will occur for every packet. Tuning/Calibrating the crystalusing the estimated CFO of the current packet to receive the next packetwill be done based on comparison with the threshold.

Otherwise, if it is determined that the CFO exceeds a threshold, controlpasses to block 260 where carrier frequency offset compensation may beperformed, e.g., in a compensation circuit such as shown in FIG. 1 .Different compensation techniques may be performed, depending uponimplementation. Once an CFO/PPM is determined at the station, the effectof crystal oscillator error can be compensated in one or more manners.In one embodiment, the crystal oscillator itself can be re-calibrated,by providing a set of programming values with a resolution to enabletuning

In another embodiment, CFO compensation may be performed by artificiallyintroducing clock and frequency offsets in a signal to be transmittedfrom a station (before transmission), such that no CFO is observed onthe final transmitted signal. Similarly, at the receiver, PPM of thecrystal may be compensated by artificially introducing the clock andfrequency offsets in the baseband such that further blocks of thebaseband do not observe the effect of PPM of the crystal.

In one embodiment, CFO compensation may be done at receiver in basebandusing a Numerically Controlled Oscillator (NCO), which can correct anegative frequency offset or positive frequency offset. Timing offsetcompensation may be done at the receiver in baseband byskipping/stuffing of a sample (in combination with fractional delayfilters).

After processing the first frame from the AP, the station knows the PPMof its crystal. The PPM of the crystal introduces frequency and timingoffset to the signal. The station, for receiving a second packet, mayoperate dedicated circuitry on the second packet from the start of thesecond packet such that the introduced frequency and timing offsets arenot observed on the frame when provided to the rest of the blocks of thereceiver. The dedicated circuitry here may contain an NCO to compensatefor the CFO introduced and skip/stuff logic (in combination withfractional delay filters) to compensate for the timing offset. If thePPM of the crystal results in the introduction of positive frequencyoffset, the NCO at the dedicated circuitry may operate to provide anegative frequency offset and vice-versa. If the PPM of the crystalresults in additional samples due to increase in sampling clockfrequency, the skip logic (in combination with fractional delay filters)of the dedicated circuitry may operate and vice-versa. In an embodiment,the dedicated circuitry may be assumed to be present after the ADC atthe receiver and before DAC at the transmitter

The station, for transmitting a packet after processing a first packetfrom the AP, may operate a dedicated circuitry on the transmit sample ofthe frame such that the frequency and timing offsets that is introduceddue to the PPM of the crystal are pre-compensated. The blocks andoperation of the dedicated circuitry may be similar to that explainedabove for receiver.

Note in implementations in which an IoT or other wireless device isoften in a sleep mode, the station may be configured to wake upperiodically for measurement and correction of PPM (calibration) toalways remain within the acquisition range.

In some cases a receiver may not successfully acquire a packet due toCFO (alone or in association with other impairments). Embodiments maystill be able to determine a CFO even where a station is outside anacquisition range.

In one embodiment, a test or hypothetical carrier frequency offset(e.g., in terms of hypothetical PPM per unit of time) may be selected.Once the station is not able to acquire packets over a certain period,then a predetermined compensation value (e.g., a PPM value) is selectedand compensated on the next receiving packet. If packet acquisitionremains unsuccessful, another compensation value can be selected (e.g.,from a set of predetermined PPM values), until the acquisition of thepacket occurs. The crystal oscillator frequency may be tuned based onthe predetermined compensation value to compensate on the next receivingpacket. The processing continues for further packets using each of thepredetermined compensation values from the set until acquisition occurs.

In another embodiment, multiple test or hypothetical carrier frequencyoffsets can be used concurrently. In this case, once the station is notable to acquire packets over a certain period, a plurality ofcorrelators, each corresponding to a compensation value (e.g., a PPMhypothesis) can be used. Note that these correlators may be implementedas a set of parallel correlators, each configured to receive an incomingdigital signal that is shifted in frequency with respect to the othercorrelators. After correlation, the hypothesis that gives a highestcorrelation may be selected as the determined CFO for the receiver, andthus may be used for performing CFO compensation. To aid in thisprocess, wider band analog and baseband filters may be used. In anembodiment, where a plurality of correlators each with a PPM hypothesisand where the bandwidth of operation of a WLAN system is 20 MHz, thewider band filters may assumed to have 10% higher bandwidth (e.g., +/−11MHz instead of +/−10 MHz)] to avoid the cutting off the edge frequencycomponents from the signal. The filter bandwidth of the wider bandanalog and baseband filter may be selected such that the adjacentchannel interference performance is within the required limit. Theadditional filter bandwidth (+/−1 MHz in above example) determines theCFO acquisition range and +/−1 MHz correspond to +/−200 PPM of a systemoperating in 5 GHz WLAN channels. With embodiments such as describedabove, signal acquisition may be achieved over a wider range of PPM/CFO.For example, embodiments may be used to acquire signals where a crystalPPM error of up to approximately +/−250 PPM occurs. Once the acquisitionis done and a PPM hypothesis is determined, then the filter bandwidthmay be reduced to the optimum instead of a wider bandwidth.

One example of such hypothetical CFO compensation is further illustratedin FIG. 2 . Specifically if it is determined at diamond 220 that signalacquisition is not successful (e.g., due to carrier frequency offset), adifferent technique may be used to identify the carrier frequencyoffset. Here at block 270 carrier frequency offset compensation may beperformed for one or more test carrier frequency offsets. For example, agiven carrier frequency offset may be assumed as this test carrierfrequency offset (note this test carrier frequency offset also may betermed a “hypothetical carrier frequency offset”).

After performing such compensation, it is next determined at diamond 280if packet acquisition is successful. If so, control passes to block 290where the test carrier frequency offset that was used for successfulacquisition may be identified. Thereafter control passes to diamond 250discussed above, to determine whether this identified carrier frequencyexceeds the relevant threshold. Instead if it is determined at diamond280 that packet acquisition still is not successful at one or more testcarrier frequency offsets, control passes back to block 270, whereanother hypothetical carrier frequency offset can be used. Note thatafter some number of unsuccessful attempts to acquire a signal usingthese test carrier frequency offsets, the method may conclude.Understand while shown with this particular implementation in FIG. 2 ,many variations and alternatives are possible.

Referring now to FIG. 3 , shown is a block diagram of a portion of abaseband processor in accordance with an embodiment. More specifically,baseband processor 300 in FIG. 3 is shown at a level of detail toidentify the components involved in performing CFO compensation onincoming packets during baseband processing. As an example, basebandprocessor 300 may be included in a receiver such as receiver 100 in FIG.1 as baseband processor 140.

As illustrated, incoming baseband signals are received in a basebandfilter 310, where they are filtered and then provided to a packetacquisition circuit 320. Packet acquisition circuit 320 may beconfigured to acquire incoming packets, e.g., based on preambleinformation. In an embodiment, packet acquisition circuit 320 may beconfigured to analyze information in the preamble of a packet todetermine CFO, such as discussed above. When acquisition isunsuccessful, acquisition may be attempted using multiple parallelcorrelation circuits 335 ₀-335_(n), as described above. In anotherembodiment, when acquisition is unsuccessful, the acquisition isattempted on further packets with each hypothetical CFO from the set,until acquisition is successful.

Still with reference to FIG. 3 , a CFO detector 330 is present andcoupled to both packet acquisition circuit 320 and correlation circuits335 such that it can determine a level of CFO. As such, CFO detector 330may output signal information and a measure of CFO, which it provides toa compensation circuit 340.

In embodiments herein, compensation circuit 340 may be configured tocompensate for the detected level of CFO. In different situations, oneor more of an NCO 342 and a sample control circuit 344 may be used tocompensate for the detected CFO. As described above, NCO 342 may providea controllable level of frequency offset based on the CFO. If avariation in PPM of a crystal results in sample variations due tovariations in sampling clock frequency, sample control circuit 344 mayskip or stuff samples (in combination with fractional delay filters).

Note that NCO 342 (or instead a direct digital synthesizer (DDS) whenpresent) may take a frequency of the waveform (e.g., sine and cosine) asan input and generate a waveform for the frequency. Here, NCO 342 mayinclude a lookup table and a digital accumulator to generate an addressin the range of the lookup table size. A series of samples selected fromthe lookup table based on the address may constitute the waveform andcan be used to mix with the signal to be frequency corrected. NCO 342may be configured to perform frequency offset compensation in thismanner. In turn, sample control circuit 344 may be configured to performtiming offset correction, e.g., by using one or more fractional delayfilters, such as a farrow interpolator.

In any event, the resulting packet information is provided to ademodulator 350 for demodulation. Note that demodulator 350 may be aseparate component from the baseband processor, such as shown in FIG. 1above. In another embodiment, demodulator 350 may be a part of thebaseband processor. Note further that one or more of CFO detector 330and compensation circuit 340 also may control various components basedon whether signal acquisition is successful and/or a level of CFOdetected. For example, a bandwidth of baseband filter 310 (as well asanalog filters not shown in FIG. 3 ) may be controlled as discussedabove. Understand while shown at this high level in the embodiment ofFIG. 3 , many variations and alternatives are possible.

As one real world example, a light bulb wireless system may work inadverse conditions, where communication itself may be very sparse andonly occur periodically. The light bulb may be a smart bulb, implementedwith one or more light emitting diodes or other light sources andincluding at least one semiconductor die that includes various controland communication circuitry, including the CFO detection andcompensation circuitry described herein.

The operating temperature of this system can be high, and thetemperature may not be the same between wake-up states. A change intemperature at the light bulb (station) causes a change in the PPM ofthe crystal present at the light bulb, which in turn results in a shiftof LO center frequency and baseband/AFE clocks derived from it. Thesechanges in turn introduce frequency offset and timing offsetimpairments, respectively, as seen in baseband processing, affectingboth transmission and reception. A high offset or difference in CFO canprevent the packets from being received properly. With embodiments, CFOcan be detected and compensated to enable acquisition of signals inadverse conditions such as high temperatures.

Referring now to FIG. 4 , shown is a block diagram of a representativeintegrated circuit 400 that includes CFO detection and compensationcircuitry as described herein. In the embodiment shown in FIG. 4 ,integrated circuit 400 may be, e.g., a microcontroller, wirelesstransceiver that may operate according to one or more wireless protocols(e.g., WLAN-OFDM, WLAN-DSSS, Bluetooth, among others), or other devicethat can be used in a variety of use cases, including sensing, metering,monitoring, embedded applications, communications, applications and soforth, and which may be particularly adapted for use in an IoT device.

In the embodiment shown, integrated circuit 400 includes a memory system410 which in an embodiment may include a non-volatile memory such as aflash memory and volatile storage, such as RAM. In an embodiment, thisnon-volatile memory may be implemented as a non-transitory storagemedium that can store instructions and data. Such non-volatile memorymay store instructions, including instructions for determining CFO andcompensating for the same, as described herein.

Memory system 410 couples via a bus 450 to a digital core 420, which mayinclude one or more cores and/or microcontrollers that act as a mainprocessing unit of the integrated circuit. In turn, digital core 420 maycouple to clock generators 430 which may provide one or more phaselocked loops or other clock generator circuitry to generate variousclocks for use by circuitry of the IC.

As further illustrated, IC 400 further includes power circuitry 440,which may include one or more voltage regulators. Additional circuitrymay optionally be present depending on particular implementation toprovide various functionality and interaction with external devices.Such circuitry may include interface circuitry 460 which may provideinterface with various off-chip devices, sensor circuitry 470 which mayinclude various on-chip sensors including digital and analog sensors tosense desired signals, such as for a metering application or so forth.

In addition as shown in FIG. 4 , transceiver circuitry 480 may beprovided to enable transmission and receipt of wireless signals, e.g.,according to one or more of a local area or wide area wirelesscommunication scheme, such as Zigbee, Bluetooth, IEEE 802.11, IEEE802.15.4, cellular communication or so forth. As shown, transceivercircuitry 480 includes a baseband circuit 485 that can perform CFOdetection and correction as described herein. Understand while shownwith this high level view, many variations and alternatives arepossible.

Note that ICs such as described herein may be implemented in a varietyof different devices such as an IoT device. This IoT device may be, astwo examples, a smart bulb of a home or industrial automation network ora smart utility meter for use in a smart utility network, e.g., a meshnetwork in which communication is according to an IEEE 802.15.4specification or other such wireless protocol.

Referring now to FIG. 5 , shown is a high level diagram of a network inaccordance with an embodiment. As shown in FIG. 5 , a network 500includes a variety of devices, including smart devices such as IoTdevices, routers and remote service providers. In the embodiment of FIG.5 , a mesh network 505 may be present, e.g., in a building havingmultiple IoT devices 510 _(0-n). Such IoT devices may perform CFOdetection and correction as described herein. As shown, at least one IoTdevice 510 couples to a router 530 that in turn communicates with aremote service provider 560 via a wide area network 550, e.g., theinternet. In an embodiment, remote service provider 560 may be a backendserver of a utility that handles communication with IoT devices 510.Understand while shown at this high level in the embodiment of FIG. 5 ,many variations and alternatives are possible.

While the present disclosure has been described with respect to alimited number of implementations, those skilled in the art, having thebenefit of this disclosure, will appreciate numerous modifications andvariations therefrom. It is intended that the appended claims cover allsuch modifications and variations.

What is claimed is:
 1. A radio device comprising: an analog front end(AFE) circuit to receive and process an incoming radio frequency (RF)signal comprising a packet; an analog-to-digital converter (ADC) coupledto the AFE circuit to receive and digitize the processed incoming RFsignal into a digital signal; a detector coupled to the ADC to detect acarrier frequency offset (CFO) in the digital signal based at least inpart on a preamble of the packet; and a controller coupled to thedetector, wherein the controller is to generate a compensation value forthe CFO based on the detected CFO, and wherein the controller is to sendthe compensation value to an oscillator to compensate for the CFO whenthe detected CFO exceeds a threshold value, and to not send thecompensation value to the oscillator when the detected CFO is less thanthe threshold value.
 2. A radio device comprising: an analog front end(AFE) circuit to receive and process an incoming radio frequency (RF)signal comprising a packet; an analog-to-digital converter (ADC) coupledto the AFE circuit to receive and digitize the processed incoming RFsignal into a digital signal; a detector coupled to the ADC to detect acarrier frequency offset (CFO) in the digital signal based at least inpart on a preamble of the packet; and a controller coupled to thedetector, wherein the controller is to generate a compensation value forthe CFO and cause one or more components of the radio device tocompensate for the CFO using the compensation value, wherein thecontroller is to generate a second compensation value when a firstpacket is not acquired, the compensation value being generated using thesecond compensation value, the second compensation value to compensatefor a hypothetical CFO in a second packet.
 3. The radio device of claim2, further comprising a frequency generator coupled to provide one ormore mixing signals used by the AFE to process the incoming RF signal.4. The radio device of claim 3, wherein the controller is to send thecompensation value to one or more of an oscillator and the frequencygenerator to cause the CFO compensation to occur.
 5. The radio device ofclaim 4, wherein the controller is to send the compensation value to theoscillator when the detected CFO exceeds a threshold value, and to notsend the compensation value to the oscillator when the detected CFO isless than the threshold value.
 6. The radio device of claim 2, furthercomprising: an oscillator to provide an oscillation signal; and afrequency generator configured to generate a mixing signal based on theoscillation signal and provide the mixing signal to the AFE forprocessing the incoming RF signal.
 7. The radio device of claim 2,wherein the controller is to generate a plurality of test compensationvalues, each of the plurality of test compensation values for thehypothetical CFO, the controller selecting the second compensation valuefrom the plurality of test compensation values.
 8. The radio device ofclaim 2, further comprising a plurality of correlators each to perform acorrelation on the second packet using a corresponding one of aplurality of test compensation values, and wherein the controller is toselect one of the plurality of test compensation values for use as thesecond compensation value for a third packet based on outputs of theplurality of correlators.
 9. The radio device of claim 8, furthercomprising one or more filters in the AFE to process the incoming RFsignal, wherein the one or more filters are to operate at a widerbandwidth when the plurality of correlators are used.
 10. A methodcomprising: receiving, in a receiver, a radio frequency (RF) signal of afirst packet; processing, in the receiver, the RF signal into a basebandsignal; in response to determining that the first packet is not acquiredfrom the baseband signal, generating at least one test compensationvalue to compensate for a hypothetical carrier frequency offset (CFO) ina second packet; controlling one or more devices in the receiver usingthe at least one test compensation value to compensate for thehypothetical CFO; and thereafter in response to acquiring the secondpacket using the at least one test compensation value, further using theat least one test compensation value to control the one or more devicesto compensate for a CFO in the baseband signal.
 11. The method of claim10, wherein controlling the one or more devices comprises sending acompensation signal based on the at least one test compensation value toan oscillator to cause the oscillator to adjust a frequency of operationof the receiver.
 12. The method of claim 10, wherein controlling the oneor more devices further comprises sending a compensation signal based onthe at least one test compensation value to a frequency generator of thereceiver to cause the frequency generator to adjust a frequency of amixing signal provided to a transmitter, the transmitter included in atransceiver with the receiver.
 13. The method of claim 10 furthercomprising: determining the CFO comprising: obtaining a preamble of athird packet from the baseband signal; extracting a first portion of thepreamble; measuring the CFO based on the first portion; and generating acompensation value of the receiver based on the CFO.
 14. The method ofclaim 13, wherein controlling the one or more devices comprises sendingthe compensation value to a frequency generator of the receiver or anoscillator generating an oscillation signal used by the frequencygenerator.
 15. The method of claim 10, further comprising: generating aplurality of correlation values, each of the plurality of correlationvalues being generated using one of a plurality of message contentsobtained using one of the at least one test compensation value; andselecting one of the at least one test compensation value based at leastin part on the plurality of correlation values.
 16. A system comprising:a receiver comprising: an analog front end (AFE) circuit to receive andprocess an incoming radio frequency (RF) signal comprising a packet; adigitizer coupled to the AFE circuit to convert the processed incomingRF signal into a digital signal; a detector coupled to the digitizer todetect a carrier frequency offset (CFO) in the digital signal, whereinthe detector is to detect the CFO based at least in part on one or morefields in a preamble of the packet; and a compensation circuit coupledto the detector to compensate for the CFO in the digital signal, whereinthe compensation circuit comprises a numerically controlled oscillator(NCO) to generate a signal corresponding to a frequency offset that isopposite to the CFO, the signal to be combined with the digital signal,or comprises a sample control circuit to compensate a timing offset ofthe digital signal based at least in part on the CFO.
 17. The system ofclaim 16, further comprising: a transmitter; and a controller to controlthe transmitter to compensate for the CFO during a communication with anaccess point, wherein the access point comprises a second transmitter totransmit the incoming RF signal comprising the packet.
 18. The system ofclaim 16, further comprising: a controller to determine a compensationvalue for the CFO based on the detected CFO and send the compensationvalue to an oscillator to cause the oscillator to adjust an oscillationfrequency of a clock signal used by the receiver.
 19. The system ofclaim 16 further comprising: an oscillator to generate a clock signalhaving an oscillation frequency; and a frequency generator configured togenerate a mixing signal from the clock signal, wherein the AFE uses themixing signal to generate the processed incoming RF signal.
 20. Thesystem of claim 19 wherein the frequency generator or the oscillator arecontrolled based on the CFO.